php iis 7.5 500 error

i manually installed PHP, following a guide http://www.peterguy.com/php/install_IIS6.html#phpConfigure. i am trying to run in on IIS 7.5

i am receiving this error:

Module: IsapiModule

Notification:   ExecuteRequestHandler

Handler:    PHP

Error Code: 0x8007007f

and i cant make heads or tails of it. i made a blank file called test.php that gives the error, a similar file called test.html, also blank, does not give an error.

i made an application pool, allowed the php5isapi.dll, etc.

NOTE: no error logs are created, although i configured php.ini to create logs in a specific folder.